Large concrete shells are being utilized increasingly in the various types of buildings. Most frequently, these are storage buildings with the concrete shell forming a roof of dome-like configuration.
One successful technique for erection of a concrete shell structure utilizes a membrane form, much like an enormous tent, for the complete shell. The form membrane is positioned over the base of a building and is inflated to afford a continuous cover of dome-like configuration. Concrete is then applied to the surface of the inflated membrane. The concrete is usually applied to the exterior of the membrane, although internal application can be utilized as disclosed in U.S. Pat. No. 3,118,010, Herrall Harrington, issued Jan. 14, 1964. Another technique for erecting concrete shells employs a multi-use form assembly comprising a structural frame with a two-layer inflatable membrane form mounted on the frame. The form assembly is aligned with a part of the building foundation, the form is inflated, reinforcing members are positioned on the external surface of the membrane form, and concrete is then deposited on the surface of the inflated form. After the concrete sets, the form is deflated and the form assembly is moved to a new position to form a further segment of the total shell. This segmental construction technique is described in Harrington U.S. Pat. No. 3,619,432, issued Nov. 9, 1971.
In the use of inflatable membrane forms for the erection of concrete shells, one of the more difficult continuing problems lies in the necessity for securing and sealing the edges of the form membrane to a building base or to a form support structure positioned immediately adjacent the foundation or other base for the building. If the edges of the form membrane are fastened down by retaining strips that use nails, bolts, or other like fasteners, tearing of the membrane is a frequent problem, particularly if the membrane is used repeatedly in constructing a multi-segment shell or in the erection of a plurality of individual shells. Moreover, such conventional fastening means make it difficult to remove the form membrane for subsequent reuse, and damage to the edge portions of the membrane almost inevitably occurs.
A releasable clamp assembly that has been used successfully for a number of years in securing the edge portions of an inflatable membrane form for use in erection of a concrete shell is described in Harrington U.S. Pat. No. 3,719,341, issued Mar. 6, 1973. That clamp assembly comprises a metal channel that is mounted on a support at the base of the shell, facing outwardly. The support is usually a part of the building. A wood rail is wrapped in the edge portion of the form membrane and is then inserted into the longitudinal opening of the channel. In the embodiment most used commercially, an auxiliary rail is positioned within the channel, below, the main rail on the outside of the fabric. That clamp assembly is quite useful and effective because it requires no nails, screws, or like fasteners. The tension on the membrane produced when the form is inflated helps to hold the rails and the membrane edge in the clamp channel. When the form is deflated, on the other hand, the form membrane can be released from the clamp channel for reuse.
The clamp assembly of Harrington U.S. Pat. No. 3,719,341, however, has some remaining disadvantages. Thus, when the form membrane is being secured to the clamp assemblies, close cooperative effort is required between two workmen, one working on the inside of the inflatable form and the other positioned outside of the form. If these two workmen are not effective in coordinating their efforts, substantial time can be lost and, on occasion, the edge portion of the form membrane may be damaged. Furthermore, that clamp assembly is limited to use with a form membrane which, when inflated, extends back over the top of the clamp channel at an acute angle. If inflation of the form produces tension in a direction outwardly of the longitudinal opening of the channel, the edge portion of the form is pulled out of the channel. Finally, the clamp assembly presents some difficulty when the concrete shell has set and removal of the form membrane is desired because the concrete at the rim of the shell usually covers the longitudinal opening of the clamp assembly channel, making it necessary to remove the entire clamp assembly before the edge of the membrane can be disengaged from the clamp.